Abstract:Heavy fermion systems can exhibit abundant attractive quantum ground states by tuning external parameters such as dimension. High-quality USb₂ thin films were prepared on graphene/6H-SiC(0001) surface by molecule beam epitaxy. Combining the reflection high energy electron diffraction, X-ray diffraction, electric transport and X-ray photoelectron spectroscopy measurements, it is demonstrated that the grown USb₂ films are high-quality single crystals. Furthermore, the surface topography, atomic structure and band structures of USb₂ films were characterized by scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPS). Results show that the surface atomic structure, electric transport property and band structure of the grown USb₂ films are similar to those of bulk USb₂ single crystals. The preparation and characterization of high-quality USb₂ films provide precious experimental experiences for exploring fantastic properties of low-dimensional uranium-based heavy fermion systems by growing ultrathin films with desirable thickness in the future.

Abstract:As an essential component in the preparation of bonded NdFeB magnets, the function of binder is to improve the fluidity of magnetic powder particles and the bonding strength, ensuring the mechanical and magnetic stability of products. The selection of binder content and its effects on the mechanical and magnetic properties of bonded NdFeB magnets were studied by combining theory with experiment. On this basis, high performance bonded NdFeB magnets were prepared. The structure and morphology of the magnet were characterized by the scanning electron microscope (SEM). The magnetic and mechanical properties of ring-shaped bonded NdFeB magnet (RSM) were measured under conditions of NIM-200C hysteresigraph and electro-mechanical universal testing machines (AG-X plus), respectively. The results demonstrate that bonded NdFeB magnet with 3wt% binder is able to achieve the highest density of 5.59 g/cm³ and the highest compressive strength of 159 MPa with the optimum value of magnetic properties.

Abstract:Tungsten oxide (WO_3-x) thin films were fabricated by reactive magnetron sputtering at glancing angle α=0° or α=80°, and then titanium oxide (TiO₂) was deposited on it. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the crystal structure, surface/cross-section morphologies, and surface chemical composition of the WO_3-x/TiO₂ thin films. Electrochromic properties of the WO_3-x/TiO₂ thin films were measured by electrochemical workstation in three-electrode system with 1 mol/L LiClO₄/PC solution and UV-Vis spectrophotometer. Results reveal that the WO_3-x/TiO₂ thin films present totally amorphous structure independent on glancing angles. As the glancing angle is kept at 80°, the nano-columnar porous thin film is obtained. Substoichiometric tungsten oxide (WO_3-x) and stoichiometric titanium oxide (TiO₂) are confirmed by XPS spectra of W 4f and Ti 2p, respectively. Compared with the dense thin film, the nano-columnar porous film needs a lower driving potential and presents faster response. The charge capacity of the nano-columnar porous film is calculated to be 83.78 mC, which is over twice higher than 30.83 mC of the dense film. The intercalation and deintercalation ion diffusion rates are determined to be D_in=5.69×10^-10 cm²·s^-1 and D_de=5.08×10^-10 cm²·s^-1 at the applied potential ±1.2 V, respectively. The electrochromic cycle of the nano-columnar porous WO_3-x/TiO₂ thin film is more stable than that of pure WO₃ thin film. The optical density varying (ΔOD) of the nano-columnar porous thin film is larger than that of the dense thin film due to the larger optical modulation amplitude in the whole visible wavelengths.

Abstract:The methods of substrate preheating, remelting and in-situ presintering were proposed to fabricate Ti-47Al-2Cr-2Nb by selective laser melting (SLM). The effects of these approaches on the formation of cracks and surface quality were investigated. The results indicate that substrate preheating, remelting and in-situ presintering powder can reduce the formation of cracks to a certain extent, and the density is increased by 1.71%~4.34%. Remelting contributes to improvement of the surface quality but greatly reduces the productivity. In addition, the combination of substrate preheating and in-situ presintering can effectively prevent the occurrence of cracks, and the density is over 99%.

Abstract:After homogenization, forging, cold rolling, and recrystallization of V-5Cr-5Ti alloy, universal testing machine, scanning electron microscopy, and transmission electron microscopy were used to study the effect of precipitates on the mechanical properties of the alloy and to estimate the strengthening effect. Results show that as-cast V-5Cr-5Ti alloy has a dendritic structure characterized by lamellar phase. After homogenization, the precipitates are transformed from a lamellar to a needle-like dendritic structure. The precipitates are broken into a short-bar or spherical phase during forging and cold rolling. The average tensile strength, yield strength, and elongation of the as-cast alloy are 505.0 MPa, 415.0 MPa, and 8.2%, respectively, with the brittle cleavage fracture as the dominant fracture mechanism. The fracture mechanism is transformed into a mixed fracturing mode of intergranular and quasi-dissociative fractures after homogenization. After 80% cold rolling and 1000 °C/1 h annealing, the average tensile strength, yield strength, and elongation of the alloy are 487.3 MPa, 382.7 MPa, and 26.2%. The alloy plasticity is greatly improved due to the refinement of the grain and precipitates. The fracture mechanism of the alloy after cold rolling and annealing is microporosity fracture. The precipitates enhance V-5Cr-5Ti alloy by Orowan strengthening mechanism. Taking the alloy after 80% cold rolling and annealing at 1000 °C/1 h as an example, the yield strength increment obtained by precipitate strengthening is about 50.1 MPa.

Abstract:The corrosion mechanism of the N10276 alloy before and after long-term aging treatment in aqueous solutions containing CO₂/Cl^- and CO₂/H₂S/Cl^- was studied through the electrochemical impedance plots and cyclic potentiodynamic polarization. Results reveal that a not-well-defined capacitive loop appears in the low-frequency range and it changes into Warburg's impedance as the H₂S concentration increases (10~100 μL/L) due to the large quantities of H₂S-related adsorbed species in the film. In addition, H₂S concentration plays a key role in increasing corrosion rate. In comparison, the action of long-term aging is more significant on pitting corrosion. The surrounding sites of the precipitates become the preferred corrosion area since the austenite microstructure of long-term aged N10276 alloy includes lots of precipitated second phases (μ phase with accumulation of Mo and Ni elements), leading to the occurrence of pitting defects.

Abstract:High nitrogen stainless steel has excellent mechanical and chemical properties. Cr-Mn-Mo high nitrogen stainless steel with a nitrogen content of 0.54wt% was smelted by increasing the content of Cr and Mn at the nitrogen partial pressure of 80 000 Pa. The sample steels after hot rolling were held at 800, 900, 1000, 1100 and 1200 °C for 1, 2, 3, 4, and 5 h. Orthogonal analysis was carried out to study the microstructure, yield strength, tensile strength, elongation to fracture, reduction of area, and product of strength and plasticity under different temperatures and holding time, in order to find the best heat treatment temperature and time for the test steel. The results show that Cr₂N precipitates in the samples without solution treatment and after solution treatment at 800 and 900 °C, and ferrite precipitates in the samples after solution treatment at 1200 °C. The materials treated at 1000 and 1100 °C are pure austenite. The specimen held at 1000 °C for 4 h has the best plasticity and high strength, and its section shrinkage and post-fracture elongation can reach 67.5% and 69.5%, respectively. The strength of the samples without heat treatment is the highest, and the reduction of section and elongation after fracture remains at 42% and 49.9%. The comprehensive mechanical properties of the samples held at 1000 °C for 1 h are the best, and the product of strength and plasticity can reach 58.59 GPa%.

Abstract:The effect of silicon contents (4wt%~8wt%) on microstructure of high-silicon austenitic stainless steel ZeCor was investigated by XRD, TEM and indentation deformation. Results show that increasing Si content leads to the phase constitute change of ZeCor alloy: the microstructure is single-phase austenite (γ phase) in ZeCor-4wt%Si alloy, γ phase with a small quantity of σ-phase in ZeCor-6wt%Si alloy, and as for the ZeCor-8wt%Si alloy, the main precipitations are Cr₃Ni₅Si₂ phase and a bit σ-phases. In addition, the Cr₃Ni₅Si₂ phase has a higher silicon and nickel content than the σ-phase. The Cr₃Ni₅Si₂ phase with a micro-hardness HV as high as 7840 MPa is a typical hard and brittle phase, and the precipitation of such phase can greatly increase the micro-hardness of the γ matrix in the ZeCor-8wt%Si alloy. The strengthening mechanism of γ matrix in ZeCor alloy is as follows: the solid solution strengthening is the main strengthening mechanism in ZeCor-6wt%Si alloy, while the solid solution strengthening of Si and the precipitation strengthening of Cr₃Ni₅Si₂ greatly increase the micro-hardness of the γ matrix in ZeCor-8wt%Si alloy, and the Cr₃Ni₅Si₂ phases have a great effect.

Abstract:Microstructure and corrosion behavior of 0.2wt% Ca and/or 0.2wt% Y modified Mg-2Zn-1Al (ZA21) rolled sheets were analyzed by SEM, XRD, hydrogen evolution and electrochemical measurement. Results show that Ca and Y refine the grains, modify the second phases, and reduce the Mn content in Mn-containing phase. In 3.5wt% NaCl solution, the preferential corrosion sites locate at the Mg-matrix near Mn-containing phases. The 12 h-corrosion rates satisfy ZA21 (8.59 mm/a)>ZA21+0.2Ca (7.17 mm/a)>ZA21+0.2Y (4.22 mm/a)>ZA21+0.2Ca+0.2Y (1.26 mm/a). The enhanced corrosion resistance of the Ca, Y modified alloys can be accredited to the follows: (1) the refinement of grain size; (2) the devitalization of the intensity of the micro-galvanic corrosion by generating low-Mn and non-Mn phases rather than the high Mn-content phases; (3) the dense, shallower cracked and more protective corrosion product film composed of Mg, Mg(OH)₂, Al₂O₃, Ca-containing and Y-containing components replaces the fully-cracked and limited protective one without Ca, Y incorperation.

Abstract:Extruded AZ31 magnesium alloy was used as raw specimens, and pre-deformation experiments were conducted in the direction of ∥ED (extrusion direction) and ⊥ED at room temperature. The instantaneous deformation stress state of a cross-sectional reduced wall was simulated in the cold Pilgering process. Then, the pre-deformed specimens were sampled for secondary compression, and the microstructure after two deformations was characterized by electron backscatter diffraction. The effects of structure and texture on mechanical behavior under the condition of strain path change were investigated. Results show that the yield strength of the AZ31 magnesium alloy is improved by pre-deformation. The improvement is attributed to the {102} tension twins resulting from the pre-deformation, further resulting in grain refinement and increase in dislocation density. Moreover, the appearance of twinning changes the grain orientation. The weakening of the basal texture (or the strengthening of the twin texture) may play an important role in improving the mechanical properties of the AZ31 magnesium alloy. The yield strength of the ∥ED-3% and ⊥ED-3% samples is increased by 66.7% and 6.6%, respectively.

Abstract:In order to simulate the hot-rolling composite technology of GH4169 superalloy, the hot isothermal compression bonding tests were performed on an MSS-200 thermal simulator in the temperature range of 900 °C to 1100 °C and at strain rates of 1~10 s^-1. The Arrhenius type constitutive equation and the hot processing map were established to describe the deformation behavior of GH4169 superalloy during the compression bonding. Furthermore, the corresponding thermal deformation activation energy Q and the stress index n were calculated as 320.33 kJ^·mol^-1 and 4.1573, respectively. Additionally, the bonding interfaces were observed by optical microscope (OM) and electron backscatter diffraction (EBSD) technique. The results show that the bonding interface is mainly affected by the technological parameters, and the bonding interface becomes almost invisible at 1100 °C with a rate of 10 s^-1.

Abstract:An optimized structure of the Si/graphite/disorded-carbon (Si/G/DC) composites was proposed and prepared to improve the cycling performance by ultra-fine grinding of elemental mixtures of nano-silicon, graphite and sucrose followed by thermal treatment. The morphology, electrochemical performance, cycling stability and optimization of silicon content of Si/G/DC composites were investigated. Results show that the use of nano-silicon materials loaded on graphite carbon matrix can effectively improve the electrochemical performance of anode materials combined with high-temperature pyrolysis technology. With graphite as buffer matrix and conductive network and amorphous carbon coating, the Si/G/DC composite shows excellent electrochemical performance. The amorphous carbon coating in the Si/G/DC composite can apparently reduce the possibility of contact loss between silicon and electrolyte, and help to maintain the mechanical stability by relieving stresses resulting from silicon volume change.

Abstract:IrO₂-Ta₂O₅-MnO_x electrodes with different Mn contents were prepared. The effect of Mn content on the physical and electrochemical characteristics of these electrodes was revealed. The results show that the coated IrO₂-Ta₂O₅-MnO_x layer has a larger specific surface area due to its bumpy and porous structure. The doping of a small amount of Mn inhibits the crystallization of the active ingredient IrO₂ and turns it into Ir³⁺. With properly replacing Ir with Mn, the electrocatalytic performance of the IrO₂-Ta₂O₅-MnO_x electrodes can be enhanced dramatically. The increased electrocatalytic activity, longer lifetime and lower cost benefit from the larger active surface area of the Mn-doped electrode, thus promoting the release of oxygen in the sulfuric acid solution.

Abstract:LiFePO₄ (LFP)/Ti3AlC₂(MXene) composites were prepared and then made into ink. Then LFP/MXene cathode was obtained by inkjet printing method. The effects of MXene content on the electrochemical performance of LFP were studied by adjusting the addition ratio of MXene to 2wt%, 3wt%, 4wt%, 5wt%, 6wt%. The results show that with the increase of MXene content, the electrochemical performance increases and then decreases. The optimal performance is obtained when the MXene addition ratio is 4wt%, at which the capacity increases to 181.2 mAh·g^-1, and the Coulomb efficiency is 99.4% after 100 cycles. The reasons are that the MXene materials have an accordion layered structure so that the contact sites of lithium iron phosphate increases, and MXene materials have more functional group structure than graphene materials, which contributes to the electrochemical performance improvement of LFP. However, if excess MXene is added, agglomeration will occur which will affect its electrochemical performance.

Abstract:The effect of Al on the microstructure and corrosion behavior of low neutron absorption cross-section Ti-Zr-Nb high entropy alloys was investigated. The phase diagram, microstructure, oxidation behavior and corrosion behavior of Ti-Zr-Nb alloys without Al addition and with ~15at% Al were compared. The phase diagram shows that below the melting temperature, Ti-Zr-Nb ternary alloys are bcc phase, and Al is inclined to form intermetallics in Ti-Zr-Nb alloys, and thus reduces the single-phase bcc temperature region in phase diagram. XRD and TEM results show that as-cast Ti-Zr-Nb ternary alloys is simple bcc structure, and Al will transform the crystal structure to ordered B2 structure. The corrosion behavior of Ti-Zr-Nb alloys was studied by thermogravimetric analysis and autoclave exposure. Results show that corrosion oxide layer formed on TiZrNb ternary alloys tends to spall during corrosion process, while Al addition will increase the stability of oxide layer without changing the main type of oxide formed during corrosion process. Oxidation kinetics was evaluated by calculating reaction rate constants and activation energies, and it is found that the high temperature oxidation property of Ti-Zr-Nb alloys with Al addition is comparable to that of Zr alloys.

Abstract:Chemical vapor deposition (CVD) method was used to prepare Nb-W binary alloy. The microstructure and mechanical properties of the Nb-W binary alloy were studied by metallographic microscopy, scanning electron microscopy, electron probe spectroscopy and microhardness tests. Results show that the resulting Nb-W binary alloy has the characteristics of a regular angle layered structure, which is mainly composed of columnar crystals with the following composition fluctuations: Nb as the matrix at the connection between the layers with Nb-W solid solution distributed around it. The Nb-W solid solution is used as the matrix in the layer around which the Nb atoms are evenly distributed. Macroscopically, the W atoms mainly form a layer along the crystal growth direction, followed by transition to Nb atoms through the NbW solid solution; microscopically, the distribution of Nb and W atoms shows the characteristics of alternating content. The layered structure of the Nb-W alloy, composition difference between the layers, and overlapping difference of the grain size between the layers were verified by finite element simulation calculations and analysis, which play a significant role in improving the mechanical properties. The CVD forming mechanism and strengthening mechanism of Nb-W alloys were also revealed.

Abstract:Nano-cutting causes internal microscopic defects in the workpiece, and this defect structure is closely related to the initial temperature of the cutting layer. In order to reduce the defects of workpieces in nano-cutting, a nano-cutting model of single-crystal copper with a cutting layer was constructed using molecular dynamics. Firstly, the applicable initial temperature of the cutting layer was determined by analyzing the changes in the structural volume and microscopic defects of the workpiece. Secondly, the effect of the initial temperature of the cutting layer on the cutting forces, dislocations and lattice was analyzed. Finally, the simulation results were indirectly verified by experiments. The results show that the applicable initial temperature range of cutting layer for single crystal copper is 293~400 K. As the initial temperature of the cutting layer increases, the transition rate of the lattice structure increases and the magnitude of the cutting force changes significantly, but the effect on fluctuations is small. When the initial temperature of the cutting layer is set in the range of 360~390 K, the surface microscopic defects of the single crystal copper workpiece are relatively less, and thus it is predicted that the surface quality of the single crystal copper workpiece is higher when it is machined in this initial temperature range.

Abstract:The original JC model, modified JC model and strain compensated Arrhenius equation were used to describe the stress-strain curves of Incoloy825 alloy at different temperatures (950~1150 °C) and strain rates (1~10 s^-1) after friction and temperature rise modification. The results show that the modified curve shows obvious characteristics of dynamic recrystallization. Compared with the original JC model and the modified JC model, the Arrhenius model of strain compensation is more suitable to describe the stress-strain behavior of Incoloy825 alloy during hot deformation. Temperature and strain rate have significant effects on the evolution of special grain boundaries. The length fraction of special grain boundary is positively correlated with the dynamic recrystallization fraction. Compared with the case of annealing after cold rolling, the special grain boundary fraction regulated by hot deformation process is relatively low. Hot deformation process is not conducive to the improvement of special grain boundary fraction, because the formation of dynamic recrystallization during hot deformation leads to small twin related domain (TRD) size.

Abstract:The densed-Ni coatings on sintered NdFeB magnets was prepared by high-energy ball milling method, and the densed-Ni coating was tested by film/substrate bonding force and Vickers hardness. The corrosion resistance of the magnets was studied by neutral salt spray test and high temperature PCT test. The corrosion process of the magnets was further analyzed by static full immersion test. The results showed that the Ni coating on the magnet surface could be densified by ball milling process. The microhardness of Ni-D24/NdFeB magnet increased from 427.95 HV to 502.67 HV and the binding force increased from 16.30 Mpa to 23.85 Mpa at 400 rpm and 24 h ball milling time, which indicated better mechanical damage resistance. The self-corrosion current density of the coating reduced by one order of magnitude compared with that of Ni/NdFeB magnet, and the resistance time to neutral salt spray increased from 312 h to 480 h, showing better corrosion resistance.

Abstract:The friction extrusion additive manufacturing (FEAM) process of 6061 aluminium alloy was successfully performed. The microstructure features, interface bonding mechanism and mechanical properties of single-pass one-layer, two-layer and nine-layer additive specimens were discussed in detail. It is found that under the process conditions of a spindle speed of 600 rpm and a moving speed of 300 mm/min, completely dense and defect-free 6061one-layer, two-layer and nine-layer additive specimens with layer thickness and width of 4 mm and 32 mm are obtained. The uniform microstructures of additive specimens are composed of fine and uniform equiaxed grains. The average grain size of one-layer and nine-layer additive specimens are 5.63±1.66 μm and 8.31±1.68 μm, which are significantly refined compared with the bar base metal (24.21±5.3 μm) . In the microstructures of single-pass one-layer additive specimen, the main strengthening phase b2 is almost completely dissolved and phase b′ is coarsed, so the average hardness is 64.7% of the bar base metal. The additive interface realizes metallurgical bonding and has the most significant degree of grain refinement. The hardness of interface reduce to 56.9% of the bar base metal because the strengthening phases b2 and b′ are almost completely dissolved. The average hardness of nine-layer specimen after multiple thermal cycles is 50.6% of the base metal. The nine-layer additive specimen exhibits excellent strength and toughness matching. The average tensile strength and elongation along the length direction of the additive specimen are 194 MPa and 34.6%, respectively, and the average tensile strength and elongation along the vertical direction of the additive specimen is 151.0 MPa and 10.4%, respectively.

Abstract:In order to investigate further the effects of vacancies, self-interstitial Fe atoms and Frenkel defects on the plastic deformation behavior of α-Fe under tensile load, the molecular dynamic models of the α-Fe samples with each type of the point defects are established and related simulations under uniaxial tension are carried out for a series of point defect atomic concentration of 0, 0.125%, 0.250%, 0.500%, 0.750% and 1.000%, respectively. The stress-strain curve is obtained, the dislocation generation and the crystal structure evolution of each α-Fe sample are observed and analyzed by using the dislocation extraction algorithm and the common neighbor analysis, respectively, and the following understandings are concluded. Different types of point defects can lead to different lattice distortion and related plastic deformation. Both the lattice distortion and related plastic deformation caused by self-interstitial Fe atoms are greater than those caused by vacancies at the same defect concentration, respectively. The changes of plastic deformation mechanisms induced by point defect types and concentrations make the characteristics of stress-strain curves change, i.e. the greater the concentration of self-interstitial Fe atom or Frenkel defect is, the less the distance between the upper and lower yield points on a stress-strain curve is, even vanishes, while the vacancy concentration has no such influence. Specifically, both the local amorphization and the related amorphization plastic deformation caused by self-interstitial Fe atoms are higher than those caused by vacancies. For the samples with low concentration of each of the three types point defects or for the samples with high concentration of vacancies, the plastic deformation is of a mixture of the tensile stress-induced phase transformation and the dislocation slip, while for the samples with higher concentration of self-interstitial Fe atoms (such as 0.500%, 0.750% and 1.000%) or with higher concentration of Frenkel defects (such as 0.750% and 1.000%), the plastic deformation is dominated by both the dislocation slip and the amorphization plastic deformation and accompanied by a little phase transition. The research in this paper deepens the understandings of the effects of point defect on the plastic deformation mechanism of metals and lay a useful foundation for the subsequent analysis of the physical and mechanical properties of polycrystalline α-Fe materials.

Abstract:The Ti6Al4V alloy powder has been successfully prepared by the multi-stage deep reduction method. In this paper, the mechanism of the magnesium thermal self-propagating reaction in the process has been explored. The products were characterized by XRD, SEM, ICP and laser particle size analyzer. The results show that Al and V elements will enter the Ti matrix as a solid solution, causing the diffraction peaks to shift to high angles. The two reaction modes of "pre-sintering-reduction-sintering" and "reduction-sintering" are the main reasons for the difference in product morphology. The volume averageD[4,3] of self-propagating products is positively correlated with the combustion temperature of the system. The remaining Mg mainly exists in the form of complexes such as MgTiO3 and MgAl2O4. These ternary composite oxides can be decomposed by metal calcium in the deep reduction stage, and finally the Mg and O in the product can be reduced to 0.01wt.% and 0.24wt.%, respectively.

Abstract:The non-isothermal oxidation tests ofthe near-α high-temperature titanium alloys (Ti150) without graphene oxide (GO) and with 0.5 wt.% GO were carried out at room temperature ~1500 ℃ by thermogravimetry-differential scanning calorimetry method. The influence mechanism of GO on non-isothermal oxidation behavior was revealed by analyzing the oxidation mass gain laws and the microstructure characteristics of oxidation products. The results showed that the non-isothermal oxidation process of Ti150 alloy with GO included almost no oxidation (≤800 ℃), slow dissolution of oxygen in α phase (800~1160 ℃), accelerated dissolution of oxygen in two-phase region (1160~1300 ℃), rapid dissolution of oxygen in β phase (1300~1330 ℃), and violent growth of oxide scale (1330~1500 ℃) five stages. The dissolution of oxygen in β phase and growth of oxide scale were the main reasons for the non-isothermal oxidation mass gain. After non-isothermal oxidation to 1500 ℃, the non-isothermal oxidation mass gain and oxide scale thickness of Ti150 alloy with GO were 10.8% and 17.9% lower than those without GO, respectively. The main mechanism of GO improving the non-isothermal oxidation resistance was that the beginning temperature of rapid dissolution of oxygen in β-Ti was delayed due to the higher β-transus temperature of Ti150 alloy with GO, which resulted in the decrease of oxygen solution, and the finer grain made the Al2O3-rich oxide layer and the Sn-rich layer more continuous and dense, which were more effective barriers to ion diffusion.

Abstract:In order to improve the wear resistance of TC4 titanium alloy, two wear-resistant composite coatings of Ni60+50%WC and d22 powder based +(Ni60+50%WC) were prepared on the surface of TC4 titanium alloy by laser cladding. Microstructure and phase composition of the coating were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The properties of the coating were analyzed by HV-1000 micro Vickers hardness tester, HRS-2M high-speed reciprocating friction and wear tester and WDW-100D electronic universal testing machine. The results show that the two coatings are composed of W₂C, TiC, Ni₁₇W₃, Ni₃Ti and Ti_xW_1-xphases; The two coatings not only exhibit excellent metallurgical bonding with the substrate, but also have uniform and dense microstructure without cracks; Due to the presence of the in-situ synthesized hard phase and fine-grain strengthening make the hardness of the coating significantly increased, which is about 2.8 times that of the TC4 substrate; The friction coefficient (COF) and wear amount of the two coatings are much lower than that of TC4 titanium alloy substrate, and the wear resistance of the two coatings is nearly 17 times higher than that of the substrate; The shear bonding strength of Ni60+50%WC composite coating and d22 powder based + (Ni60+50%WC) composite coating are 188.19 MPa and 49.11 MPa respectively. Conclusion: Both coatings can significantly improve the hardness and wear resistance of the TC4 titanium alloy substrate surface, and Ni60 + 50% WC composite coating performs better in hardness, wear resistance and bonding strength.

Abstract:In order to effectively solve the problem of bacterial infection and the release of harmful metal ions after long-term implantation of biomedical titanium alloys in the human body, Graphene oxide coating (GP/T) and Graphene oxide/Nano-zinc oxide composite coating (GZP/T) were prepared on the surface of Ti6Al4V alloy pretreated by Polydopamine(PDA) respectively with hydrothermal reaction and coating methods. The phase structure, microstructure, corrosion properties in Ringer"s solution and antibacterial properties in Escherichia coli environment of the two coatings were systematically analyzed. The results show that Polydopamine plays the role of "double-sided tape" bridging and effectively enhances the chemical bond between the coating and the substrate. The antibacterial rate of GP/T coating increased with GO concentration increasing. The GZP/T nanocomposite coating has superior corrosion resistance compared with Ti6Al4V substrates, and the ZnO in the composite coating plays a major antibacterial effect.

Abstract:Based on the molecular dynamics method, the uniaxial tensile simulation of the bicrystal TiAl alloy containing voids is performed. The evolution behavior of defects and acoustic emission(AE) response on the deformation TiAl alloy and fracture of the TiAl alloy are studied at nanometer scale. The results show that the size and location of the voids have little influence on the elastic modulus of the TiAl alloy and the yield strength decreases with the increase of the void size. After plastic deformation, twin boundary can block dislocation emitted continuously at the edge of void, and increase crystal strength. When yield stress is reached, the TiAl alloy with voids at grain boundary is more likely to produce stable dislocation structure, which hinders the movement of other dislocations, thus improving the crystal strength. Through the analysis of the AE signals during the stretching process, it is found that the AE signals mainly come from lattice vibration, and has a large power range and a lower median frequency. The AE signals of dislocation slip reveal the characteristics of wide frequency domain, and the AE signals of dislocation proliferation and dislocation accumulation display the characteristics of low power. The AE signals of crack propagation belongs to the burst signal, which is characterized by high frequency and high power.

Abstract:In this paper, Ti(N)-TiBw composites were prepared by spark plasma sintering (SPS) with pure Ti powder and BN powder as raw materials. The effect of annealing temperature on microstructure evolution and mechanical properties of Ti(N)-TiBw composites was studied. Results show that Ti and BN react in situ to form dense TiBw and N solution strengthened titanium matrix composites when sintered at 1000 ℃. TiBw is distributed in the primary particle boundary in the form of needle like network. With the increase of heat treatment temperature, the aspect ratio of TiBw first increases and then decreases, reaching the maximum at 1100 ℃. However, when the annealing temperature is above 1100 ℃, TiBw coarsens gradually, and the microstructure changes from needle shape to short rod shape. The pinning effect of TiBw on the matrix is obviously weakened, and the grain size of Ti matrix coarsens gradually. The morphology evolution of TiBw follows Ostwald ripening mechanism. As the heat treatment temperature increases, the ultimate tensile strength of the composites first increases and then decreases, reaching a maximum value of 908 MPa at 1000 ℃. The strength improvement is attributed to grain refinement, TiBw load transfer and O/N solution strengthening.

Abstract:As an important high-temperature thermoelectric materials, SiGe alloy has been concerned and used widely. Although the dimensionless thermoelectric merit (ZT) of n-type SiGe alloys thermoelectric material has made much great progress, the ZT of p-type SiGe alloys is still low. In this paper, p-type Si80Ge20Bx (x = 0.5, 1.0, 2.0) alloys thermoelectric materials were prepared by one-step alloying method using Si, Ge and B powders as raw materials. The composition, microstructure and thermoelectric properties of the samples were characterized and analyzed. The results show that, in-situ one-step alloying followed by spark plasma sintering can be realized and bulk materials can be obtained. With the increase of B doping content, the electrical conductivity increases significantly and the thermal conductivity decreases significantly. When the temperature is 950 K, the thermal conductivity is 1.79 W/(m K). At 1050 K, ZT reaches the maximum value of 0.899. Due to the synergistic effect of ball milling and doping, different types of defects are produced in SiGe structure matrix resulted in scattering of different wavelengths of phonons, leading to the decrease of thermal conductivity of SiGe alloy.

Abstract:The effects of trace yttrium (yttrium content 0.025%, 0.05%, 0.075%, 0.1% respectively) and T6 treatment on the microstructure and properties, on the eutectic transformation temperature of Al-7Si-0.3Mg alloy were studied by tensile test, hardness test, microstructure analysis of OM, SEM (+EDS), XRD and DSC. The tensile test and hardness test showed that the YS, UTS and E1% of the aluminum alloy after yttrium microalloying were improved, and the comprehensive performance with 0.05%Y was the best among the designed aluminum alloys. The microstructure and composition analysis showed that the strengthening phases were mainly Si and Mg2Si phase, and Mg2Si phase usually appeared with Si phase. DSC analysis showed that the added yttrium decreased the transformation temperature of α_Al+β_Si→Liquid, and it decreased 1.1℃, 2.0℃, 1.4℃ and 2.2℃ respectively when 0.025%, 0.05%, 0.075% and 0.1% Y was added respectively. In addition, the transformation temperature of α_Al→Liquid was increased somewhat after Yttrium microalloyed. An appropriate amount of yttrium that formed multiple phases with βSi, Mg2Si and so on, which promoted the formation of heterogeneous nucleation substrate, and improved the supercooling in solidification.

Abstract:The effects of shot peening and shot peening combined vibration finishing on the fatigue properties of GH4169superalloy are studied contrastively. The surface morphology, surface structure, roughness, microhardness and residual stress field of the sample were analyzed by scanning electron microscope, roughness profiler, microhardness tester, and X-ray stress tester, and the internal relationship and mechanism of surface integrity and fatigue performance are discussed. The internal relationship between surface integrity and fatigue properties and its mechanism were discussed. The results show that the composite treatment can improve the fatigue performance better. The composite treatment increases the room temperature fatigue strength of GH4169superalloy by 21.6％. Preheating at 500℃for 100h reduces the fatigue strength of composite strengthened GH4169superalloy by 6％, but it is still 14.29％ higher than that of the base material. That is to say, the composite treatment can effectively improve the fatigue resistance of GH4169superalloy under high temperature working conditions from room temperature to 500℃.

Abstract:In order to study the dynamic mechanical properties of 2219 aluminum alloy, dynamic compression experiments were carried out through split Hopkinson impact pressure bar (SHPB) equipment on 2219 aluminum alloy in two heat treatment states (T4 and T6). The microstructure of the obtained samples is analyzed by OM and XRD. It is found that the flow stress of the material decreases significantly when the strain rate exceeds 2000 s-1 under the two heat treatment conditions, that is, a significant strain rate softening behavior occurs. Based on the two-dimensional contour map of strain rate sensitivity behavior with real strain and strain rate, it is found that the material exhibits negative strain rate sensitivity behavior under the condition of high strain and high strain rate, and the flow stress decreases with the increase of strain and strain rate. Through theoretical calculation and microstructure characterization, it is found that the softening effect caused by temperature rise softening and lamellar grain breakage is an important reason for the negative strain rate sensitivity behavior of the material at a high strain rate and high strain rate.

Abstract:The microstructure evolution of beryllium which was deformed at the temperature of T = 350 ℃ and the strain rates of ε? = 10_^-3?s_^-1 was systematically studied during annealing by mean of hot compression and vacuum annealing experiment. The annealing temperature is from 680 ℃ to 880 ℃. The results show that the metal beryllium has a unique static recrystallization behavior. The new grains first occur bulge at the {10 2}<10 > tensile twin boundaries. The bulge mechanism is similar to prior grain boundary bulge by strain induced grain boundaries migration in the vicinity of prior grain boundaries. The pinning effect of BeO impurities on the prior grain boundary migration is the reason why the twin boundary bulge nucleation precedes to the grain boundary bulge nucleation. The twin boundary bulge nucleation and grain boundary bulge nucleation are the main nucleation mechanism of the metal beryllium static recrystallization, supplemented with intragranular nucleation and the particle stimulated nucleation of recrystallization. When annealed from 680 ℃ to 880 ℃, the beryllium deformed at 350 ℃ low temperature is able to achieve complete recrystallization microstructure of grain refinement, no recrystallization texture is formed in the recrystallization microstructure. Similarly, the recrystallization grains of the metal beryllium are difficult to grow due to the pinning effect of BeO impurities on grain boundary migration. Annealing at 680 ℃, 730 ℃, 780 ℃, 830 ℃ and 880 ℃, the recrystallization time is about 2160 min, 180 min, 20 min, 5 min and 4 min, respectively. The metal beryllium occurs {0001} basal plane slip and {10 2}<10 > twin deformation under compression at 350 ℃. The deformation mechanisms are same as that at room temperature, no change with temperature the increase of temperature, and keep typical abnormal deformation behaviors of the metal beryllium.

Abstract:The cracks will impact the toughness and wear properties in the coating formation process of micro-arc oxidation melting and cooling. This paper uses the ZrO₂ strength and toughness to prepare ZrO₂/MgO coating with self-repairing cracks, and investigates the effect of in-situ ZrO₂ on the wear properties of the coating. The research found that the in-situ synthesis ZrO₂ by micro-arc oxidation undergoes phase transition in the high-temperature discharge channel to generate volume expansion and micro-cracks initiation at the interface of zirconia, which inhibits the crack propagation during the coating formation process and realizes the role of self-repairing coating cracks.The ZrO₂ content in the coating can be regulated by controlling the content of the zirconium source, the in-situ ZrO₂ content in the coating is 32%, the cracks of the ZrO₂/MgO coating are finely dispersed, and the crack density is 63.4% lower than that of the traditional coating, the friction coefficient is reduced by 53.4%, the amount of wear descended by 66.7%. Research thinks, the in-situ synthesized ZrO2 self-repairing cracks and improvement of wear resistance during the coating preparation process, which can reduce the friction coefficient and mass loss, and improve the surface wear properties of the ZrO₂/MgO coating.

Abstract:Using the experimental data obtained by isothermal and constant strain rate compression of the SP700 titanium alloy under the Gleeble-3800 thermal simulation test machine, the instability map based on the Prasad instability criterion is constructed. The boundary conditions for the thermal compression instability deformation of SP700 titanium alloy when the deformation temperature is 700 ~ 950 ℃ and the strain rate is 0.001 ~ 1 s_^-1 are obtained. Based on this, combined with Deform-3D finite element software to analyze the SP700 titanium alloy in the process of hot compression, the distribution and change of the unstable deformation area are studied by finite element numerical simulation.The results show that the microstructure of the SP700 titanium alloy obtained by the hot compression experiment is in good agreement with the finite element numerical simulation results. The Deform-3D finite element software can effectively simulate and predict the distribution and change of the unstable deformation area of the SP700 titanium alloy during the hot compression process.

Abstract:The superplasticity, gas bulging forming properties and microstructure of LZ91 Mg-Li alloy sheet were studied by hot tensile test, gas bulging forming experiment, metallographic analysis and scanning electron microscope observation. The results show that the rolled LZ91 alloy sheet exhibits excellent superplasticity: the elongation is up to 343.7% and the strain rate sensitivity index is 0.697 when the hot tensile temperature is 573 K and the strain rate is 0.001 s-1. Under the conditions of bulging temperature of 573 K and bulging pressure of 0.06 MPa, the sheet forming height is 51.14 mm and the height-diameter ratio is 1.279, which indicates that the Mg-Li alloy sheet has good superplastic forming potential. Dynamic recrystallization occurs in both hot tensile and superplastic gas bulging forming, it can effectively improve the plastic forming ability of the alloy. The typical superplastic cavities morphology at both tensile fracture and bulging fracture shows that the main deformation mechanism is grain boundary slip, and the main cause of superplastic failure is the growth and connection of the cavity.

Abstract:In this paper, TiO2@SiO2 composite materials with different Ti contents were prepared. The microscopic morphology, crystal structure, chemical composition and optical properties of TiO2@SiO2 composite materials were analyzed by SEM, XRD, BET, XPS ,DRS and spectral analysis method, and photocatalytic degradation experiments were carried out. The results showed that the sample is anatase TiO2 with a spherical core-shell structure, a large specific surface area and blue shift of light response range. XPS showed that the Ti-O-Si bond is formed between TiO2 and SiO2. Ti-O-Si bond contributed to the separation of photogenerated electrons holes, and further promoted the generation of superoxide radicals in active oxygen during the photocatalytic degradation process. Due to defects and distortions produced at the interface between TiO2 and SiO2 phases, there are more oxygen vacancies were generated at the interface, thereby organic pollutants are degraded. The degradation processes of methyl orange and rhodamine B dyes were compared, it showed that the adsorption of the composite material has a significant effect on the degradation rate and degradation pathways of the dye molecules. The negative potential on the surface of the composite material strongly adsorbs the diethylamino group of the RhB molecule and dissociates the group first, and it promotes the occurrence of the characteristic blue shift effect of the solution. The synergistic effect of adsorption and active oxygen accelerates the degradation of dye molecules. The scavenger experiment also proved that the superoxide radical is the most important active substance in the degradation process of MO and RhB dye solution under visible light, and other kinds of active oxygen play an auxiliary role. The research content of this work reveals the adsorption and degradation process of different dyes, and promote the application of photocatalytic technology in sewage treatment。

Abstract:Tensile experiments were conducted at different temperatures for the Haynes 230 nickel-based alloy, and the microscopic mechanism of the tensile deformation behavior at high temperatures was investigated using Electron Backscattered Diffraction (EBSD) technique.It is shown that Haynes materials have a high resistance to plastic deformation until 800℃. At 650℃, the materials show a significant dynamic strain aging (DSA) phenomenon, and the DSA effect is similar at 700℃ and 800℃, and the DSA effect is weakest at 760℃.The strengthening effect of DSA effect makes the alloy still maintain high strength at 650℃, and the tensile strength at 800℃ does not decrease much compared with that at 760℃.The EBSD results show that a large number of deformed twins appear near the fracture at room temperature, and the grain orientation is dominated by <111>; the <111> orientation of the tissue near the fracture is more obvious at 650℃, and the grain boundaries are bent and deformed, which increases the resistance to dislocation movement; with the increase of temperature, dynamic recrystallization grains appear in the intergranular and intracrystalline areas near the fracture.

Abstract:Thin strips of Nd(FeTi)₁₂/ɑ-Fe and Nd(FeTiNb)₁₂/ɑ-Fe alloys were prepared by vacuum arc melting and melt quenching processes to investigate the effects of the addition of Nb elements and different nitriding temperatures on the microstructure and magnetic properties of the alloys. The results show that the addition of Nb elements significantly refines the grain size and increases the amorphous formation rate of the alloy. The magnetic properties of Nd(FeTiNb)₁₂N/ɑ-Fe strips were significantly increased after crystallisation annealing and nitriding, and the best magnetic properties were achieved at a nitriding temperature of 500 °C, when the remanent magnetisation (Br) and coercivity (Hcj) were 21.9 emu/g and 700 Oe, respectively.

Abstract:In this paper, pure tungsten (W) and tungsten lanthanum(W-La) spherical powders were prepared by using plasma rotating electrode atomization powder technology (PREP). The chemical composition, morphology, physical properties, defects and particle size distribution of the two types of powders were compared and analyzed. The results show that the spherical pure W powder prepared by the PREP method has a smooth surface and high sphericity, and the yield of powders smaller than 106 μm is 70%.Most of the La2O3 volatilizes during the PREP process after adding to the bar,and the remaining La2O3 preferentially adheres to the surface of the droplet, which reduces the surface tension of liquid metal tungsten and increases the yield of powders smaller than 106μm to 90%. However, the decrease in surface tension also causes a small number of defects on the surface of the W-La powder. The phenomenon of La2O3 increasing the powder yield provides a new idea for the study of improving the powder yield of PREP technology.

Abstract:The corrosion behavior of Mg-6Zn, Mg-6Zn-1Ca and Mg-6Zn-1Mn alloys in Phosphate Buffer Saline (PBS) solution were studied by XRD, SEM, EDS, 3D profilometer and weight loss method, and the corrosion mechanism of the three alloys were discussed. The results show that the addition of Ca and Mn can reduce the weight loss rate of the alloy, but the weight loss rate of the alloy with Mn addition (W_r=3.91 % after immersed for 10 days) is lower than that of the alloy with Ca addition (W_r=6.78 %), indicating that Mn element has better corrosion resistance to PBS, which is related to the formation of dense oxide film on the surface of the alloy with Mn addition. At the same time, Mg-6Zn-1Mn alloy shows that pitting corrosion is caused by the primary battery composed of the second phase and the matrix. After solution treatment at 420 °C for different holding time (2~20 h), the corrosion pit of the alloy surface decreases with the increase of holding time, indicating that long time solution treatment can reduce the galvanic corrosion between the second phase and the magnesium matrix, and increase the tendency of uniform corrosion of the alloy.

Abstract:In this paper, GNPs/Al composites were prepared by mechanical stirring and sintering method. The complete spreading of non-destructive GNPs and uniform distribution of GNPs in aluminum matrix were realized. The effect mechanism of GNPs on the densification behavior of composite powder during cold pressing and sintering was studied. The effect mechanisms of GNPs on the strength and plasticity of composite was clarified. The effect of sintering time on the mechanical properties of GNPs/Al composite was discussed. The results showed that the relative density of sintered GNPs/Al composite was more than 98% when the content of GNPs was less than 0.5%. The yield strength of as sintered Al-0.5wt.% GNPs reached 204 MPa, which is 18.6% higher than that of pure aluminum. Taking Al-0.5wt.% GNPs as an example, after sintering for 6h, the hardness of the composite was 61.5HV and the yield strength was 173 MPa. No obvious failure occurred at the compression strain being 40%.

Abstract:Potassium rhenate was obtained from the solution after precipitation of tungsten and molybdenum by potassium chloride precipitation reaction. Then potassium rhenate solution was converted into perrhenic acid solution by ion exchange method. Finally, high purity ammonium rhenate was obtained by ammonia neutralization - concentrated crystallization - recrystallization. The results show that KCl solid is added to the solution after precipitation of W and Mo, and then concentrated to precipitate KReO₄ white crystal. The contents of main impurities Na, Ca, Fe and Cl in potassium rhenate are less than 1%, especially W and Mo are less than 0.1%, and the crystallization rate of Re can reach 94% ~ 98%. K is removed by dynamic method with C160 (H^₊ type) resin. When the pH of KReO₄ solution is neutral and the flow rate of feed is 2 BVs.h^_-, the K ^₊ penetration capacity and saturation capacity of C160 resin are 117.865 g.L^_-1 and 128.385 g.L^_-1, respectively, and the utilization rate of resin reaches 91.81%. The concentrations of K, Na, Ca, Fe, W, Mo and Mg in the obtained pure HReO₄ solution are all below 0.5 mg.L^_-1. The HReO₄ solution is neutralized by adding high - grade pure ammonia, controlling the end-point pH to 7 ~ 8, and then concentrated and crystallized with one recrystallization. The purity of the obtained ammonium rhenate is more than 99.99%, of which the SEM morphology is dendritic.

Abstract:Micro-arc oxidation coatings were prepared on AZ91D magnesium alloy by changing the collocation of Na₂SiO₃, NaOH, KF and NaAlO₂ based on simplex-centroid mixture design. The effects of electrolyte components on the formability and corrosion resistance of the coating were investigated. The results show that the obtained regression equation is very significant and has high prediction accuracy. Pareto analysis shows that the four electrolytes have significant effects on the corrosion resistance of the coating. Response surface analysis shows that increasing the concentration of Na₂SiO₃ or NaAlO₂ can significantly improve the corrosion resistance of the coating. But the combination of the two is detrimental to the improvement of the corrosion resistance. The main salt is very important for increasing the coating formability and corrosion resistance. When the electrolyte does not contain the main salt, the coating formability and corrosion resistance are very poor. The appropriate increase of NaOH and KF concentration in the electrolyte containing the main salt is also beneficial to improve the corrosion resistance. According to Pearson correlation analysis, the corrosion resistance primarily depends on the coating density and porosity, and is also affected by other characteristic parameters such as thickness and composition. The components of the electrolyte affect the properties of the coating through influencing the above microstructure parameters.

Abstract:As we all know, lithium iron phosphate (LiFePO4) is a cathode material for lithium-ion batteries. It has received widespread attention due to its large discharge capacity, low price and no pollution to the environment. This article aims to prepare lithium iron phosphate and corresponding composite cathode inks with excellent performance suitable for microelectronic printers. Configured different concentrations of lithium iron phosphate inks and prepare electrodes, and used it to study the electrochemical performance of the electrodes prepared from the optimal concentration inks. Studies have shown that when the current density is 0.1 C, the specific discharge capacity of the lithium iron phosphate electrode with a printing concentration of 10% is as high as 142 mAhg-1, and the coulombic cycle efficiency reaches 92%; based on the poor conductivity of lithium iron phosphate, a small amount is selected to be added Reduce graphene oxide to improve its conductivity. The research results show that when the mass fraction of reduced graphene oxide is 0.6%, the discharge specific capacity of the composite material of lithium iron phosphate and reduced graphene oxide reaches 152.1 mAhg-1, and the Coulomb cycle efficiency is 99.2%. It shows that the introduction of reduced graphene oxide is beneficial to improve the overall performance of the material.

Abstract:The effects of three heat treatment regimes and two cooling ways on the microstructure and tensile properties of IMI834 titanium alloy were studied. An optical microscope was used to analyze the evolution of the microstructure of the alloys in different heat treatment states; Image-Pro Plus v5.1 (IPP) and Nano Measuer image analysis software were used to calculate the size of equiaxed α phase (α_p) and secondary α(α_s) clusters in the microstructure; The crystal orientation and the deformation behavior of the alloy in situ before and after deformation were characterized using in-situ SEM tensile test and EBSD technology. The fracture morphology of the material in the different cooling speeds was analyzed using scanning electron microscope.The distribution of second phase was analyzed by TEM. The results show that:in the double annealed test,with the increase of the first annealed temperature,the content and the size of α_pgradually decreased,but the secondary α clusters increased.With the increase of the first annealed temperature, the strength of IMI834 alloy first increased and then decreased. The elongation and reduction of area did not change significantly.When the first annealed temperature is 1020℃, the strength of IMI834 titanium alloy reaches the highest under the two test conditions of sample heat treatment (rapid cooling) and block heat treatment (slow cooling).The strength of the sample heat treatment (rapid cooling) is higher than that of the block heat treatment (slow cooling) by about 50 MPa; In the early deformation stage of IMI834 alloy, the crystal rotation angle of fast cooling is generally higher than that of slow cooling;The existence of the β phase between the α_pand α_s can ensure that the slip transfer can still be carried out under low geometric compatibility factor; The quasi-cleavage facets of the fracture surface under fast cooling conditions is ellipsoidal or polygonal, and under slow cooling conditions, it is elongated. The difference of the distribution of second phase in the α/β bounderies is the reason for the different morphologies.

Abstract:The laser-MAG hybrid welding of 08Cr19Mn6Ni3Cu2N with low nickel and nitrogen content was carried out using 92% Ar+8% N2and 95% Ar+5% CO2 as shielding gas. The mechanism of the effect of shielding gas on the microstructure and properties of the welded joint was investigated. The results show that the average microhardness of the weld decreases with the addition of nitrogen, the welding spatter increases with the increase of arc volume and the decrease of arc stability, and the ferrite content in the weld decreases from 14.1% to 10.9% , the ferrite Dendrite also became finer and the secondary dendrite arm became shorter. There are only a few phases and two phases in the weld, and no phases and nitrides are found. The size of austenite grain decreases with the addition of nitrogen from four crystal planes.

Abstract:Five groups of diamond-like carbon (DLC) films with different arc currents were deposited on cemented carbide substrates by arc ion plating (AIP), aimed at the preparation of the super-hard ta-C film. The in?uences of arc current on the phase structure, microstructure, carbon atoms bond, mechanical properties and friction behavior of DLC ?lms were studied from various measurement tools, such as scanning electron microscope, Raman spectroscopy, X-ray photoelectron spectrometry, nanoindenter and ball-on-disk tribometer, respectively. The re-sults indicated that when the arc current is the lowest at 30 A, the surface of DLC film is the most smooth and compact, and the number of large particles in the least. The minimal ratio ID/IG and the maximum sp3 bond content are 0.87 and 64% at the arc current of 30 A, respectively. The ta-C film exhibits excellent performance including the highest hardness and modulus of 56.7 GPa and 721.1 GPa, the highest elastic recovery coefficient of 58.9% and the lowest friction coefficient is 0.073 while arc current is 30 A. However, the surface of the film becomes loose and porous, and the number of large particles on the surface increase with the increase of arc current. The ratio ID/IG increases and sp3 bond content decreases with increasing arc current. The hardness and modulus of DLC films decrease gradually, the ratio H/E changes little and H3/E2 decreases, and the friction co-efficient increases with increasing arc current. In summary, the results show that when the arc current is smaller, the ta-C film with super hard tetrahedral amorphous can be prepared by arc ion plating, and has excellent com-prehensive properties.

Abstract:The galvanic corrosion of SS 304-Al 6061 in 30% nitric acid environment and the influence of different area ratios of cathode and anode on the corrosion process of SS 304-Al 6061 were studied by immersion and electrochemical experiments. The surface morphology, number of corrosion pits and electrochemical parameters of Al 6061 before and after corrosion were measured and analyzed by means of SEM, EDS and electrochemical measurement. The results show that the corrosion driving potential difference between Al 6061 and SS 304 reaches 583 mVSCE, and Al 6061 is used as the reaction anode to dissolve corrosion. It can be seen from SEM images that there are three kinds of galvanic corrosion phenomena after coupling, among which the micro-galvanic corrosion caused by the second phase particles coupled with the aluminum matrix is the main type of corrosion pits. Meanwhile, the increase of the area ratio of cathode and anode leads to the decrease of the galvanic potential and the increase of the corrosion current. The galvanic current and the area ratio of cathode and anode satisfy the quantitative relationship, and the theory is in good agreement with the practice by K-S test.

Abstract:The preparation of high performance aluminum alloy by semi-solid forming technology is one of the important research directions of aluminum alloy forming technology, and then the present status of aluminum alloy semi-solid forming technology is reviewed from aluminium alloy material using, semi-solid pulping process and application. then, research results: aluminum alloy obvious grain size, size is more uniform, the preparation of the fine equiaxial recrystallization organization of semi-solid slurry, obtain better mechanical properties. Finally, point out the problems in the current research, the future development direction of semi-solid forming of aluminum alloys is prospected.

Abstract:Bile duct stent implantation is one of the important methods for the treatment of bile duct obstruction caused by benign bile duct stenosis and malignant tumors. The material function and surface structure of the implanted stent are particularly critical to its service performance. At present, the commonly used biliary stents are divided into two categories: metal and plastic. The existing statistics on the treatment of biliary diseases show that the accumulation of microorganisms and the inflammation caused by them are common problems in the treatment of stent implantation. Therefore, the development of antibacterial multifunctional bile duct stent materials and new stents is particularly urgent. Ag nano particle is an excellent antibacterial and antibacterial material, which is widely used in the field of medical materials. The bionic superhydrophobic structure and nano silver coating modify the surface of the implantable medical bile duct stent, which can effectively solve the problem of bacterial growth and secondary blockage of the biliary tract. This article describes the common preparation methods of nano-silver coating and hydrophobic structure on the surface of bile duct stents, and summarizes the latest developments in the research of bile duct stents and surface coatings by analyzing the development of bile duct stents, coating technology and medical application practice of superhydrophobic structures, and prospect the trend of bile duct stent and its coating materials.